1. Field of the Invention
The present invention relates to an organic polymer which is easily crystallized, a process for preparing the same and a photoconductive material and a spatial light modulator comprising the same.
2. Description of the Related Art
Recently, organic materials having photoconductivity are vigorously developed and studied as photoconductive materials which are used in an electrophotographic printer or an optical printer.
Among the photoconductive materials, polyvinyl carbazole (hereinafter referred to as "PVK") is well studied. PVK has a high carrier transporting ability of holes, for example, a hole mobility of up to 10.sup.-5 cm.sup.2 /Vs at room temperature. The carriers in a film are supposed to hop on the carbazole rings which are helically bonded to a polymer backbone and move along the backbone.
A polymer layer consisting of PVK alone has no light absorption band in the whole visible light region. However, addition of an equimolar amount of electron-accepting trinitrofluorenone to PVK makes it possible to exchange carrier charges with the carbazole rings to form a carrier moving complex, whereby a sensitive region is expanded over the whole visible light region.
Now, there is mainly used a function-separated type photoconductor comprising a laminated carrier-generating layer which generates carriers through absorption of light and a carrier-transporting layer which effectively transports the carriers. As a carrier generating material, an inorganic material such as Se, As.sub.2 Se.sub.3 and the like; a deposited layer of an organic material such as phthalocyanine compounds; or a coated layer comprising a binder and a squalium salt dispersed therein is used. As the carrier-transporting material, various organic materials such as a composition comprising a binder and a triphenylamine derivative dispersed therein are developed in addition to PVK.
As a material having a high carrier transporting ability, there has been proposed polyparaphenylene sulfide (hereinafter referred to as "PPS") (see U.S. Pat. No. 4,886,719). Although PPS is an excellent insulating material having good heat resistance, its carrier transporting ability can be considerably increased by heat treatment in oxygen gas (see the preprint for the 35th Lecture Meeting of the Association Relating Applied Physics Society, 31p-A-11). This may be because the oxygen molecules trapped in the film weakly bond the PPS molecules and penetrate into an amorphous region so as to bond the molecules in the crystal region. Then, it is assumed that, in such PPS, a direction of carrier transportation is perpendicular to the molecular chain and PPS has high carrier mobility in the crystal region.
It is possible to greatly increase orientation and crystallinity of oligomer phenylene sulfide having an oligomerization degree of 5 to 7 (hereinafter referred to as "OPS") by vapor deposition. It is found that photoconductivity of the deposited OPS film is increased by enlargement of the crystal region and a direction of carrier transportation is perpendicular to a major axis of the molecule (see the preprint for the 41st Lecture Meeting of the Applied Physics Society, 5p-ZH-15). Therefore, it would be possible to transport the carriers which are generated by light absorbance in a light absorbing band for the above functional group along the OPS backbones, if a film having good orientation and crystallinity were produced from OPS molecules in which a carrier-generating functional group is incorporated (see Japanese Patent Kokai Publication No. 120747/1990).
Similar to PVK, PPS and OPS have limited absorption regions in a short wavelength range of not longer than 400 nm. According to the above proposals, it is possible to increase sensitivity in the visible light region by constructing a function-separated type photoconductor through lamination of the carrier-generating layer and a carrier-transporting layer made of the above material.
However, PPS and OPS have a problem that a carrier injection efficiency is unsatisfactory.
In case of PVK, it has been tried to introduce a sensitizable functional group directly to a side chain instead of the carbazole group. However, since it is difficult to achieve high crystallinity of a product, the sensitivity cannot be increased.
Among liquid crystal spatial light modulators, a modulator comprising a photoconductive layer which comprises amorphous silicon or CdS and a nematic liquid crystal in laminated state is proposed as an optically addressable spatial light modulator.
In the spatial light modulator comprising a combination of the photoconductive layer and the liquid crystal, an orientation state of the liquid crystal is controlled by light irradiation through the photoconductive layer. When an inorganic photosensitive material such as the amorphous silicon or CdS is used in the photoconductive layer, a ratio of a light receiving area of the photoconductive layer to a liquid crystal pixel area and a film thickness are designed so that the layer performs a switching function. That is, they are designed so that a dielectric constant of the liquid crystal .epsilon..sub.LC and a dielectric constant of the photoconductive layer .epsilon..sub.pH satisfy the following relationship:
.epsilon..sub.LC S.sub.LC /d.sub.LC &lt;.epsilon..sub.PH S.sub.PH /d.sub.PH
wherein S.sub.LC is an area of the liquid crystal, d.sub.LC is a depth of the liquid crystal, S.sub.PH is is an area of the photoconductive layer and d.sub.PH is a depth of the photoconductive layer.
For example, in case of a photoconducting layer comprising amorphous silicon having .epsilon..sub.PH of about 11, when .epsilon..sub.LC is about 3 and d.sub.LC and d.sub.PH are assumed to be about 5 .mu.m and about 1 .mu.m, respectively, S.sub.LC : S.sub.PH is about 1:0.1. Therefore, disadvantageously, incident light is not effectively used.
Since there is an oriented film which is an insulating film between the photoconductive layer and the liquid crystal layer, charge storage on an interface is a problem.